Optical methods for detecting biological and chemical analytes, such as absorption, fluorescence, and Raman spectroscopy, have a number of applications in detecting analytes in liquid, imaging fluorescing particles, microfluidic devices, optical sensors, and bio-agent detection.
Anti-resonant waveguides are effective for guiding light inside a liquid in a fluidic channel. It is especially useful for fluorescence excitation within fluidic channels since it enables efficient use of excitation light, excitation of large area/volume, and it provides excellent stray light suppression. However, due to the special geometry of an anti-resonant waveguide, the light coupling is complicated. Dependent upon the coupling parameter, a stable and homogeneous light distribution may be achieved when a certain coupling length in the liquid is exceeded, typically about 10-100 times the waveguide thickness. With regard to bleaching of the fluorescence signal, it is necessary that excitation of the analyte is mainly concentrated to the detection area. Any interaction between excitation light and analyte prior to the detection area typically reduces the performance due to attenuation of excitation light, e.g., absorption or scattering, enhanced stray light, bleaching of fluorophores, and light induced analyte modifications.